Workpieces that need to be preheated before welding, such as cast iron, are heated to very high temperatures in an appropriate oven. After preheating, the workpiece might be welded through the oven door. This method maintains the heat of the workpiece, but results in an overly hot work environment and inconvenient access to the workpiece, which will necessitate cumbersome heat resistant gear to be worn by the workers.
Alternatively, the workpiece might be removed from the oven and placed on a steel or brick surface. In this circumstance the workpiece is more accessible, but work must be done quickly, before the workpiece cools below the temperature at which quality work may be done.
A still further alternative is to use insulating blankets to maintain the workpiece at the desired temperature. However, such blankets tend to wear at a rapid rate, resulting in excessive cost.
And as a still further alternative, other methods such as a firebrick enclosure may be used. However, such alternatives also fail both to provide a cool workplace and to provide the time required to work prior to cooling of the workpiece.
In some circumstances, additional heat may be applied to the workpiece, apart from the heat of the welding torch. While such supplemental heat may allow a greater period during which the workpiece may be available, the heat tends to result in an overly hot workplace which also tends to limit the duration of actual work.
Unfortunately, none of the above alternatives is completely satisfactory. Where the workpiece is cool enough to be easily approachable, the welding torch might not be able to maintain enough heat and welding quality is compromised. Where the welding torch is able to keep a portion of the workpiece warm, but other portions cool, warping and cracking may result. Similarly, if the part is allowed to cool too quickly, warping and cracking may also result.
Additional problems result when the welder needs to reposition a workpiece, such as a large engine block, during the course of work. Repositioning the workpiece can require several people in some circumstances, due to the heat radiated by the workpiece and due to its mass. Time spent in repositioning the work piece results in a reduction in the time during which welding may be performed.
As a result of the above problems, what is needed is a holder for a workpiece that is fully insulated and which therefore is able to prolong the time during which a welder may work. The structure of the holder should also be adapted to allow rotation about an axis in each of two perpendicularly oriented directions. The structure of the holder should also result in an opening through which work may be done that is adjustable in both size and location. The structure of the holder should also include a restraint assembly to prevent undesired movement of the workpiece within the holder.